Spill prevention system with safety valves

ABSTRACT

The present invention is for a spill prevention system to prevent fuel spills from a connecting line connecting duel fuel tanks on a truck when the connecting line is severed or detached from one of the reducer fittings to which it is attached. The connecting line provides pressure communication between the fuel tanks so that fuel flows from one tank to the other whenever there is an unequal pressure acting on the fuel, which occurs whenever one tank has more fuel in it than the other. The connecting line connects to the reducer fitting located on each fuel tank. A safety valve is immersed in the fuel in each tank and connected to the reducer fittings. Each safety valve is configured to shut off flow to the connecting line when the connecting line is severed or detached from the one of the reducer fittings.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application relates to Provisional Application No. 60/707,908 filedAug. 12, 2005, and is a continuation-in-part application of U.S. patentapplication Ser. No. 11/220,080 filed Sep. 6, 2005 now U.S. Pat. No.7,258,131.

BACKGROUND OF THE INVENTION

Most large tractor/trailer type trucks (trucks) have duel fuel tanks forincreased fuel capacity and the fuel tanks are located on both sides ofthe truck. It is important to balance the fuel weight on a truck becausean unbalanced weight on either side of the truck may cause the truck tooverturn on a sharp curve. A connecting line fits onto reducer fittingsand runs between the two fuel tanks to put the fuel tanks in pressurecommunication with one another. There is a net flow of fuel passing fromone tank to another only whenever there is a differential pressurecaused by one tank having more fuel than the other. Thus, with theconnecting line connecting the two tanks, there is never an imbalance inthe fuel weight for very long.

A problem arises whenever the connecting line between the fuel tanks issevered or detached from the reducer fittings to the fuel tanks, whichoften happens in a wreck or when the truck runs over road debris.Whenever the connecting line is severed or detached from the reducerfittings, fuel is spilled onto the ground causing environmental damageand creating a fire hazard. In fact, many truck drivers who haveaccidents lose their life not due to the damage caused by the accident,but due to fire when their fuel is spilled onto the road and ignited.

It is to solving these problems and others that the present invention isdirected.

BRIEF SUMMARY OF THE INVENTION

The present invention is for a spill prevention system to prevent fuelspills from a connecting line connecting duel fuel tanks on a truck whenthe connecting line is severed or detached from one of the reducerfittings to which it is attached. The connecting line provides pressurecommunication between the fuel tanks so that fuel flows from one tank tothe other whenever there is an unequal pressure acting on the fuel,which occurs whenever one tank has more fuel in it than the other tank.The connecting line connects to the reducer fittings located on eachfuel tank. A safety valve is immersed in the fuel in each tank andconnected to the reducer fittings.

Each safety valve has a piston assembly with a first disc-shaped piston.The first disc-shaped piston has a diameter slightly smaller than thehousing diameter so that the first piston freely slides within thehousing. The first piston has at least one orifice defined in the firstpiston. The first piston has an upstream face and a downstream face.

Each piston assembly also has a second disc-shaped piston positioneddownstream from the first piston. The second piston has a diametersubstantially equal to the first piston diameter. The second piston hasat least one orifice defined in the second piston. The second piston hasan upstream face and a downstream face. Fluid entering the safety valvehousing exerts a fluid force on the first piston and the second pistonin the direction of fluid flow.

Each piston assembly has a shaft connecting the first piston to thesecond piston. A valve stem extends from the downstream face of thesecond piston, the second piston being attached to a first end of thevalve stem. A stop is attached to a second end of the valve stem.

Each safety valve also has a valve seat with an opening substantiallyshaped and sized to matingly receive the stop. Each safety valve alsohas a spring positioned in the housing against the downstream face ofthe second piston so that the spring exerts a spring force on the secondpiston in a direction opposite the general direction of fluid flow. Whenthe fluid forces acting on the piston assembly sufficiently exceed thespring force acting on the downstream face of the second piston, thepiston assembly moves in the direction of fluid flow until the stopengages the valve seat and substantially shuts off the fuel flow to theconnecting line.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial cross-sectional view of a safety valve positioned inthe open position constructed in accordance with a preferred embodimentof the present invention.

FIG. 2 is a partial cross-sectional view of a safety valve positioned inthe closed position constructed in accordance with a preferredembodiment of the present invention.

FIG. 3 is the cross-section 3-3 shown in FIGS. 1 and 2.

FIG. 4 is a cross-sectional view of a piston assembly constructed inaccordance with a preferred embodiment of the present invention.

FIG. 5 is a flow chart for designing a safety valve in accordance with apreferred embodiment of the present invention.

FIG. 6 is a flow chart for making and assembling a safety valve inaccordance with a preferred embodiment of the present invention.

FIG. 7 is a flow chart for assembling a piston assembly on a threadedrod in accordance with a preferred embodiment of the present invention.

FIG. 8 is a schematic representation of a safety valve of the presentinvention installed on a gasoline pump.

FIG. 9 is a partial cross-sectional view of a fuel spill preventionsystem constructed in accordance a preferred embodiment of the presentinvention.

FIG. 10 is an side elevation view of a fuel spill prevention systemconstructed in accordance with a preferred embodiment of the presentinvention.

FIG. 11 is a circuit schematic view of an alert system constructed inaccordance a preferred embodiment of the present invention.

It is noted that the cross-hatching of a cross section is not intendedto indicate the use of a particular material for any of the drawings.

DESCRIPTION

FIGS. 1-2 show cross-sectional views of a safety valve 100. FIG. 1 showsthe safety valve 100 in an open position and FIG. 2 shows the safetyvalve 100 in a closed position. The safety valve 100 includes a housing102 with an inner wall 104. The housing 102 is made from a pipe oflarger diameter than a diameter of inlet piping 106 upstream of thesafety valve 100 and a diameter of outlet piping 108 downstream of thesafety valve 100. The safety valve 100 is connected to the inlet piping106 by an inlet coupler 110 and to the outlet piping 108 by an outletcoupler 112. Fluid flows through an inlet passage 111 defined in theinlet coupler 110, into the housing 102 and, when the safety valve 100is in the open position, though an outlet passage 113 defined in theoutlet coupler 112. The inlet coupler 110 and the outlet coupler 113each have a hexagonal portion with six flat sides 115 to accommodate astandard wrench.

A disc-shaped first piston 114 and a disc-shaped second piston 116 arepositioned in the housing 102, with piston outer walls 118 and 120having diameters slightly smaller than a diameter of the housing innerwall 104. There are gaps between the piston outer walls 118 and 120 andthe housing inner wall 104 that are generally small, but large enough toallow for free sliding of the pistons 114 and 116 within the housing102. The pistons 114 and 116 are separated by a shaft 122 of lengthL_(SH). The first piston 114 has a downstream face 124 and an upstreamface 126. The second piston 114 has a downstream face 128 and anupstream face 130.

A spring 132 is positioned in the housing 102 between an outlet couplerinner face 134 and the downstream face 128 of the second piston 116. Thespring 132 resiliently restrains the sliding of the pistons 114 and 116in the direction of the outlet coupler inner face 134. The spring 132has a spring constant K and a length L_(SP).

A valve stem 136 of length L_(VS) extends from the second pistondownstream face 128 to support a stop 138. The valve stem 136 isattached at a first end to the second piston 116 and at a second end tothe stop 138. As shown in FIGS. 1 and 2, the stop 138 may be integrallyformed with the valve stem 136, such as in a casting. The stop 138 mayalso be a separate piece attached to the valve stem 136. The valve stem136 is rigidly attached to the second piston 116 so that movement of thesecond piston 116 causes a like movement of the valve stem 136 and thestop 138. A valve seat 140 is defined in the outlet coupler 112. Thevalve seat 140 is shaped and sized to receive the stop 138 to form asubstantial fluid seal between the stop 138 and the valve seat 140.

As best seen in FIG. 3, orifices 142 are defined in the first piston114. There are two orifices 142 shown in FIG. 3, but if more orifices142 are required, it is recommended that the orifices 142 be spacedequally about the circular first piston 114. For example, if threeorifices 142 are required, the orifices 142 should be spaced withcenters at one hundred-twenty degree angles from one another, and with acenter of each orifice 142 having the same distance from a center of thefirst piston 114. The symmetry of the orifices 142 in each piston 114and 116 is recommended so that the fluid flow field across a diameter ofthe housing 102 does not develop asymmetries. The second piston 116generally has orifices 142 defined in positions identical to the firstpiston 114, but more or less orifices 142 may be provided in the secondpiston 116 if so desired.

A piston assembly 144 is defined to include the first piston 114, thesecond piston 116, the shaft 122, the valve stem 136 and the stop 138.The orifices 142 are defined in the piston 114 and 116 to allow the flowof fluid past the pistons 114 and 116 under normal operating conditions.The selection of the size and the number of orifices 142 is discussedbelow in greater detail.

For the embodiment shown in FIGS. 1-2, the valve seat 140 is made fromthe outlet coupler 112 that has been externally threaded to fit intointernal threads defined in the safety valve outer wall 104. The valveseat 140 has been chamfered to form a geometry that more closely matchesthat of the stop 138, thus forming a tighter seal between the stop 138and the valve seat 140.

In one embodiment, the stop 138 and the valve seat 140 have metallicsurfaces. Thus, when the stop 138 moves into the valve seat 140, theseal formed by the stop 138 and the valve seat 140 is not an absoluteseal. However, the seal so formed substantially blocks the flow of fluidinto the outlet piping 108 until a shutoff valve upstream of the safetyvalve 100 can be closed.

In another embodiment, at least one of the stop 138 and the valve seat140 are made from a resilient material so that a tighter seal is formedbetween the stop 138 and the valve seat 140. However, the resilientmaterial selected for the stop 138 or the valve seat 140 must notdegrade over time in the presence of the fluid in the piping system.Such resilient materials may include rubber, polymers, plastics, orfibrous material.

The materials generally used to make components for the safety valve 100may be any suitable material for the transport of the fluid. In the casewhere the fluid is natural gas, such materials as steel, stainlesssteel, aluminum, copper, brass and various alloys thereof may be used.Generally, it is expected that the safety valve 100 may be in a naturalgas pipeline for decades without the piston assembly being moved to theclosed position. Thus, it is highly desirable for the material selectedfor use be resistant to rust and corrosion. Such materials includealuminum, stainless steel, composites and alloys thereof. Specialconsideration in the selection of materials must also be made when thevalve is used in a high temperature or a low temperature environment andwhen the fluid flowing through the safety valve has a high or lowoperating temperature. In some applications involving high precision,the piston assembly may be made from light-weight carbon fibermaterials.

In other applications, such as water transport, the safety valve 100 mayalso be made of the metallic materials listed above, but also may bemade from plastic, polymers, or composite materials.

In operation, an excess flow rate caused by a leaky appliance or acatastrophic failure of piping downstream of the safety valve 100creates a loss of pressure downstream of the safety valve 100, which inturns creates a pressure difference between the upstream piping 106 andthe downstream piping 108. This pressure difference causes the pistons114 and 116 to slide in a direction aligned with the fluid flow throughthe safety valve 100. Thus, the piston 116 is pushed toward the valveseat 140 by the fluid flow forces, with the fluid forces exerted on thepistons 114 and 116 being counteracted by the force exerted by thespring 132 on the second piston 116. When the piston 116 moves towardthe outlet coupler 112, the stop 138 in turn moves toward the valve seat140. As shown in FIG. 1, the stop 138 is generally frustro-conical inshape. However, the stop 138 may be any shape so long as it is shapedand sized to matingly engage the valve seat 140. When the pressuredifference between the inlet piping 106 and the outlet piping 108exceeds a critical pressure difference, the stop 138 seats in the valveseat 140, the safety valve 100 is in a closed position and fluid flowthrough the safety valve 100 stops, as represented in FIG. 2.

It is well known that a breaker box for an electrical supply line shutoff the supply to an electrical circuit provided to a house when thecurrent exceeds a certain level. Similarly, the safety valve 100 closeswhen the flow rate through the valve exceeds a certain critical flowrate.

The use of the first piston 114 and the second piston 116 spaced apartby a shaft 122 allows one to use a much lighter piston assembly, ascompared to a solid-body piston with elongated holes, as taught by U.S.Pat. No. 5,215,113, issued to Terry on Jun. 1, 1993 (Terry). Because thepistons 114 and 116 are disc-shaped, it is also much easier to drillthrough the pistons 114 and 116 to create the orifices 142, as comparedto the difficulty for drilling holes in the solid-body piston.

The use of two spaced-apart pistons 114 and 116 attached to a shaft 122is a more stable structure, with respect to keeping the valve stem 136and the stop 138 in the middle of the housing 102, as compared withusing a single disc-shaped piston with a valve stem and stop. Generally,it is expected that the two disc-shaped pistons 114 and 116 will haveless friction with the inner walls of the housing 104 than would theouter edges of the solid-body piston assembly taught by Terry, becausethe two spaced-apart pistons 114 and 116 would generally have less of atotal surface area in contact with the housing inner wall 104.

Another advantage over the solid-body piston is that two disc-shaped,spaced apart pistons are much lighter than a solid body occupying thesame volume. This is particularly important when the safety valve 100 isused in an application requiring high precision in low pressure gaspipes. These applications occur, for example, when one wishes to monitorhome appliances for excess gas flow.

For these applications, one wishes to know when excess gas is flowing toan appliance because it may indicate a leak in the appliance or one ofthe appliance's gas fittings. By using a low-mass piston assembly inconjunction with a very low spring constant, the safety valve 100 may beused to sense and respond to very small changes in pressure. It is wellknown in fluid mechanics that for a given flow geometry and fluid, thepressure can be directly correlated to a flow rate. Thus, the safetyvalve 100 may be designed to shut down the flow when a small increase ingas flow rate occurs downstream of the safety valve.

Reducing the mass of the piston assembly makes the safety valve 100 moresensitive to small pressure changes in part because the fluid forcesacting on the piston assembly 144 must overcome inertia to move thepiston assembly 144 from the open position to the closed position.Reducing the mass of the piston assembly 144 would clearly lessen theamount of force required to overcome the inertia of the piston assembly144.

It is also recommended that, for applications requiring high precision,the safety valve 100 should be installed on piping in the horizontalposition. Otherwise, the weight of the piston assembly 144 may affectthe flow rate at which the safety valve will close. If the valve isinstalled in a vertical position, the weight of the piston assembly 144must be accounted for in selecting a spring 132 and an orifice size 142for the first piston 114 and the second piston 116.

FIG. 4 shows a cross sectional view of another embodiment of the pistonassembly 144 of the safety valve 100. In this embodiment, the pistonassembly 144 is made from generally off-the-shelf mechanical hardwareand piping hardware. In FIG. 4, a threaded rod 150 is used to form athreaded shaft 152 and a threaded valve stem 154 for the safety valve100. A first flat washer 156 and a second flat washer 158 acts as thepistons 114 and 116 shown in FIGS. 1-3. An internally threaded nose cone160 screws onto an end of the threaded rod to act as the stop 138 tomatingly with the valve seat 140. The flat washers 156 and 158 aresecured on the threaded rod 150 by tightening a first nut 162 against asecond nut 164 on the threaded rod 150, with two lock washers 166 andone of the flat washers 156 and 158 positioned between the two nuts 162and 164.

The flat washers 156 and 158 have holes 168 defined therein throughwhich fluid flows. In operation, the threaded rod 150 acts identicallyto the valve stem and shaft shown in FIGS. 1-2, with the flat washers156 and 158 being the first piston 114 and the second piston 116. Thenose cone 160 acts identically to the stop 138 of FIGS. 1-2 to matinglyengage the valve seat 140 to stop the fluid flow when the force exertedby the fluid on the flat washers 156 and 158 sufficiently exceeds theforce exerted by the spring 132.

FIG. 5 shows a flow chart for a method for designing the safety valve100 of the present invention. For this flow chart, the steps of themethod may be carried out in any order except where one step necessarilyprecedes another step. The method begins at step 200.

At step 202, a designer specifies the normal operating conditions forthe safety valve 100, such as the pipeline size, the fluid flowing inthe pipeline and a range of normal pipeline pressures and normal flowrates. At step 204, the designer specifies the material to be used forthe safety valve 100 based on the fluid flowing in the pipeline. At step206, given the normal operating conditions, the designer specifies adesired critical pressure difference between the pressure upstream anddownstream of the safety valve 100, above which the safety valve 100 isdesigned to close. The designer may also express this critical pressuredifference as a critical flow rate based on predetermined correlationsand measurements.

At step 208, the designer selects a safety valve housing nominaldiameter D_(H) and length L_(H). At step 210, the designer selects aspring 132 with spring constant K and length L_(SP). The spring lengthL_(SP) is selected so that the spring 132 is under a slight compressionor “preload” when the spring 132 and piston assembly 144 are assembledin the housing. The exact amount of the preload will vary depending onthe particular application. At step 214, the designer selects twopistons, each having a diameter slightly smaller than the internaldiameter of the housing 102. At step 216, the designer selects a numberN of orifices 142 having diameters of D_(O). For a safety valve 100 of agiven size, the selection of the number of orifices 142, the orificediameter D_(O), and the spring constant K determine the criticalpressure difference and the critical flow rate at which the safety valve100 will close.

The spring length L_(SP) and the spring constant K will determine thestroke S that the pistons will travel between open and closed positionsof the valve for a given housing length L. The stroke S should be of asufficient length to prevent the safety valve 100 from repeatedlyopening and closing when the pressure difference across the safety valveis near the critical pressure difference. The design of the pistonassembly 144, with a relatively long valve stem length L_(VS) and arelatively long spring length L_(SP) prevent the valve from opening andclosing when the valve is operating near the critical pressuredifference and critical flow rate. Generally, the stroke S should benominally 15-20% of the uncompressed length L_(SP) of the spring 132,and should in all cases be less than one third of L_(SP). The purpose ofthis restriction on the stroke S is to ensure that the spring 132deflects only in the linear range, so that the deflection of the spring132 as a function of force can be reliably determined.

In selecting the number of orifices 142 and the orifice size D_(O), itis also generally desirable to minimize the pressure drop across thesafety valve 100 with the safety valve 100 in the open position whileinsuring reliable operation of the safety valve 100. It is expected thatthis pressure drop will increase with decreasing size of the orifice142, but this is a general rule subject to exceptions for particulardesigns.

In one embodiment, the first piston 114 has more than two orifices 142and the second piston 116 has two orifices 142, and the size of theorifices 142 in the first piston 114 is smaller than the size of theorifices 142 in the second piston 116. In this embodiment, the firstpiston 114 acts as a filter to remove to remove contaminants from thefluid stream. In another embodiment, a fluid screen is placed in thepipeline upstream of the safety valve to remove contaminants before theyreach the safety valve 100. When the fluid being pumped through thepipeline is known to have contaminants, it is important to have amechanism to remove the contaminants or the contaminants may block theorifices 142.

As a rule of thumb, it has been found that the safety valve 100 operateswell for a gaseous fluid when a sum of the areas of all the orifices 142is 2 to 3 times less than the area of the inlet passage 111.Furthermore, it is generally believed that two orifices 142 on eachpiston 114 and 116 are sufficient for proper operation of the safetyvalve 100 in a gas pipeline.

At step 216, the designer must specify the length L_(VS), of the valvestem 136. The length L_(VS) of the valve stem 136 is selected so thatthe spring 132 fits between the second piston 116 and the outlet couplerinner face 134, applying a predetermined force to the second piston 116to prevent the stop 138 from engaging the valve seat 140. Finally, atstep 218, the designer specifies the shape of the stop 138 and valveseat 140. The method ends at step 220.

Following the method for designing a safety valve 200, a manufacturermay conduct tests and generate a series of tables to make the selectionof the safety valve 100 simply a matter of looking up in a table whichsafety valve 100 is required for a particular application. The designermay choose many of the design criteria based on experience, rules ofthumb, and other imprecise rules of design. However, assuming that allthe other criteria are determined, the choices of the number oforifices, the orifice diameters and the spring constant will determinethe critical flow rate at which the safety valve 100 will close

For a first example, assume that all the design criteria are knownexcept the orifice size and spring constant are known. Table 1 providesan example of the type of correlation between the orifice size, thenumber of orifices 142, and the spring constant K. One can look at Table1 and determine the orifice size required for the safety valve to closeat the desired critical flow rate for various combinations of springconstant and the number of orifices.

Another example of the type of correlation that can be determinedexperimentally is shown in Table 2. For Table 2, it is assumed that allthe other design criteria have been specified except the orifice size,the critical flow rate, and the spring constant. From Table 2, if one isgiven a particular orifice size and a critical flow rate, one can thendetermine the spring constant to use to cause the safety valve to closeat that critical flow rate.

It must be noted that none of the actual numerical values given byTables 1 and 2 have yet been determined. These tables are only meant todemonstrate the types of experimental correlations that a manufacturercan provide to designers to assist designers in the design of the safetyvalve 100 for particular applications.

FIG. 6 shows a flow chart for a method of making and assembling thesafety valve 100. The flow chart begins at step 300. The steps for themethod of making and assembling the safety valve may be performed in anyorder, except where one step necessarily follows another step. At step302, the person making and assembling the safety valve 100 (maker)provides a safety valve housing 102 larger than the size of the pipingto which the safety valve 100 is attached. The safety valve housing 102is a length of pipe made from a material suitable for the fluid beingtransported in the piping.

At step 304, threads are defined in the safety valve housing 102. Thethreads may be internal or external threads. As shown in FIGS. 1-2, thethreads on the safety valve housing 102 that attach the housing to theinlet and outlet couplers 110 and 112 are internal. At step 306, themaker provides an inlet coupler 110 to connect the safety valve housing102 to the inlet piping 106.

For the embodiment shown in FIG. 1-2, the inlet coupler 110 and theoutlet coupler 112 are: (1) externally threaded on one end to connect tothe internal threads on the housing and (2) are internally threaded onthe other end to connect to externally threaded inlet and outlet piping.For the case where the safety valve is retrofitted to an existing fluidline, one would expect to cut a section of the existing fluid line intwo places, remove the section of fluid line between the two cuts,thread ends of the existing fluid line where the cuts have been made,and install the safety valve. Various pipe couplers are available for:(1) connecting two externally threaded sections of pipe; (2) to connectan internally threaded pipe to another internally threaded pipe; or to(3) connect an externally threaded pipe to an internally threaded pipe.The choice of whether to use internal or external threads will dependlargely on the application for which the piping is being used.

At step 308, the maker provides an outlet coupler 112. In someembodiments, the outlet coupler 112 is made of cast material, such asaluminum and a valve seat 140 is shaped and sized in the outlet coupler112 when the outlet coupler 112 is cast to matingly receive the stop138. In other embodiments, the outlet coupler 112 is provided as anoff-the-shelf item from a hardware supplier. For this embodiment, thevalve seat 140 is defined in the outlet coupler 112 by using appropriatetools to chamfer an edge of a the outlet passage 113 until a portion ofthe valve seat is conical in shape to matingly receive the stop 138. Oneappropriate tool for chamfering the edge of the passageway is a rotarygrinding tool. After the valve seat 140 is defined in the outlet coupler112, the outlet coupler 112 is then attached to the safety valve housingat step 310

At step 312, the maker provides a spring 132 designed in accordance withthe method shown in FIG. 5 and inserts the spring 132 into the safetyvalve housing 102 against the outlet coupler 112.

At step 314, the maker provides and assembles a piston assembly 144. Thepiston assembly 144 includes the shaft 122, the valve stem 136, thefirst piston 114, the second piston 116, and the stop 138. In oneembodiment, the piston assembly 144 is cast as a unitary casting, withthe orifices 142 defined in the casting. In a second embodiment, thepiston assembly 144 is cast as a unitary casting and the orifices 142are drilled into the unitary casting.

FIG. 7 is a flow chart for yet another embodiment of a method forperforming step 314 in FIG. 6. Referring briefly to FIG. 7, the methodbegins at step 314A. At step 314B, a threaded rod 150 is provided forattachment of several components of the piston assembly 144. At step314B, the flat washers 156 and 158 are drilled to define holes 168. Atstep 314C, the first nut 162 is screwed onto the threaded rod 150 to apredetermined thread location. At step 314D, the lock washer 166 isinserted on the threaded rod 150 against the first nut 162. At step314E, the first flat washer 156 is inserted onto the threaded rod 150against the lock washer 166. At step 314F, a second lock washer 166 isinserted onto the threaded rod against the first flat washer 156. Atstep 314G, the second nut 164 is screwed onto the threaded rod 150 andtightened against the second lock washer 166. At step 314H, the steps314C through 314G are then repeated for the second flat washer 158 toattach the second flat washer 158 to the threaded rod 150 at apredetermined location. At step 314I, the internally threaded nose cone160 is screwed onto the threaded rod 150. The method stops at step 314Jand the making of the piston assembly 144 is complete.

Returning to FIG. 6, at step 316, the maker inserts the piston assembly144 into the safety valve housing 102 against the spring 132. At step318, the inlet coupler 110 is screwed into the safety valve housing 102.A length L_(PA) of the piston assembly 144 and the spring length L_(SP)should be selected so that the inlet coupler 110 slightly compresses thespring 132 when the inlet coupler 110 is screwed into the safety valvehousing 102. It is in attaching the inlet coupler 110 that the preloadis applied by the amount that the inlet coupler 110 is screwed into thethreads on the housing 102.

At step 320, the safety valve 100 is attached to the inlet piping 106and the outlet piping 108 to complete the installation of the safetyvalve 100 in the piping system. For each attachment of the safety valve102 to the inlet coupler 110, and the outlet coupler 112, and for theattachment of the inlet coupler 110 and the outlet coupler 112 to theupstream piping 106 and the downstream piping 108, it is recommendedthat the attachment be made using a wrench that fits onto two of theflat sides 115 of the hexagonal portion of the inlet coupler 110 and theoutlet coupler 112. The method stops at step 322.

FIG. 8 shows a schematic representation of a gasoline dispensing system401, with a safety valve 400 of the present invention installed at agasoline pump 402. Gasoline exits the gasoline pump 402 via the pumpexit piping 404. The exit piping 404 acts as the inlet piping 106 to thesafety valve 100 shown in FIGS. 1-2. Gasoline exits the safety valve 400through the safety valve outlet piping 406, which is connected to aflexible hose. The safety valve 400 is configured internally exactlylike the safety valve 100, and acts to shut off the flow of gasolinewhen there is a break in the piping downstream of the safety valve 400.Thus, a catastrophic failure occurs downstream of the safety valve 400occurs when a motorist drives off from the gasoline pump 402 with a fillnozzle still in his automobile gasoline tank. When the catastrophicfailure occurs, the safety valve 400 shuts down the flow of gasoline tothe nozzle.

Although the example shown in FIG. 8 and discussed in the precedingparagraph is for a gasoline pump, the same principles apply to a fillstation for an LP gas tank.

FIG. 9 is a partial cross-sectional view of a spill prevention system501 having a safety valve 100 installed in one of two fuel tanks 500 ofa truck, where the safety valves 100 are in an opposed relationship withone another. The safety valve 100 shown in FIG. 9 is identical to theembodiment shown in FIGS. 1-2 between the inlet coupler 110 and theoutlet coupler 112. The inlet piping 106 of FIGS. 1-2 is not necessarybecause the safety valve 100 is immersed in the fuel of the fuel tank500. Furthermore, instead of being connected to outlet piping 108 as inFIGS. 1-2, the outlet coupler 112 is connected to a reducer fitting 504that penetrates a wall 502 of the fuel tanks 500.

The reducer fitting 504 is threaded externally at both ends and isthreaded internally at the end having a larger diameter than its otherend. The outlet coupler 112 screws into the internal threads of thereducer fitting 504. The reducer fitting 504 screws into threads definedin a tank wall 502 and connects to a connecting line 510. The connectingline 510 is connected to the reducer fitting 504 by a hose coupler 508,which is in turn attached to the connecting line 510.

As best seen in FIG. 10, the connecting line 510 extends from thereducer fitting 504 on one fuel tank 500 to a like reducer fitting 504on a second fuel tank 500. The second fuel tank 500 has a safety valve100 configured exactly like the safety valve 100 on the first fuel tank500 shown in FIG. 9. A trip wire 512 is attached to the connecting line510. The trip wire 512 is connected to the electrical system of thetruck and is configured to indicate to a truck driver in a cab of thetruck whenever the trip wire 512 is broken.

In operation, fluid is allowed to pass through the safety valves 100 andthe connecting line 510 under normal operating conditions to evenly drawfuel from both tanks 500. This is desirable because an unbalanced loadon a truck may cause the truck to have an accident. This allows fuel toflow from one tank 500 to another tank 500 if there is a difference inthe amount of fuel in each tank 500. The pressure driving the flow wouldbe the incremental static head pressure that occurs in one tank 500 whenthat tank 500 has more fuel than the other tank 500. The restriction dueto opposing safety valves 100 causes the fuel transfer rate to be lowerthan the critical flow rate that would cause one of the safety valves100 to close.

However, if the connecting line 510 breaks or is detached from one ofthe reducer fittings 504, each safety valve 100 senses the change inflow rate through each safety valve 100, by way of the increased thepressure difference between each safety valve's inlet coupler 110 andits respective outlet coupler 112, which causes each safety valve 100 toclose. As discussed above for the safety valve 100, with all otherdimensions of the safety valve 100 being constant, the spring constantK, the number of orifices 142, and the size of the orifices 142 can bevaried to produce a safety valve 100 that closes at a precise flow rate.The precision with which the safety valve 100 operates is largely due tothe fact that the piston assembly 144 can be designed to have a very lowmass.

For the embodiment shown in FIGS. 9-10, the fuel tanks 500 could containany liquid and would be referred to simply as liquid storage tanks ifthe liquid storage tanks did not contain fuel. Furthermore, the fueltanks 500, the connecting line 510 and the spill prevention system 501may be collectively referred to as a fuel tank system or a containmentsystem.

The connecting line 510 may be a flexible hose or a rigid conduit. Thematerial which the connecting line 510 is made from is determined by theparticular liquid that is contained in the liquid storage tanks. If theconnecting line 510 is a flexible hose, suitable materials from which tomake the flexible hose include rubber, plastic, and other flexiblematerials. If the connecting line 510 is a rigid conduit, suitablematerials for the rigid conduit include steel, aluminum, rigid plastics,and various alloys thereof

FIG. 11 shows an electrical schematic for an alert system 520 to be usedin conjunction with the trip wire 512 to alert a driver of the truckthat the trip wire 512 has been broken. In FIG. 11, electrical wiringfor the alert system circuit 520 is shown by solid lines, while the fueltanks 500 and the connecting line 510 extending between the fuel tanks500 are shown by dotted lines. The alert system 520 is powered by thetruck battery 522.

A negative terminal 524 of the battery 522 is connected to any suitableelectrical ground for the alert system circuit 520, such as a frameelement of the truck. An electrical wire 526 leads from a batterypositive terminal 528 to a branch line 527 having a sensor and indicatordevice (indicator) 530. Another electrical wire 532 leads from theindicator 530 to the electrical ground for the alert system circuit 520.Yet another electrical wire 534 leads from the branch line 527 and isconnected to a first end of the trip wire 512. Still another electricalwire 536 leads from a second end of the trip wire 512 to the electricalground.

In operation, in normal operating conditions when the trip wire 512 isintact, electrical current passes through the trip wire 512 and theindicator 530 remains inactive. When the trip wire 512 is broken, theindicator 530 senses an increase in electrical current and activates toalert the truck driver that the trip wire 512 is broken. The indicator530 may include a simple light, a flashing light, or an audible signalthat indicates to the driver that the trip wire 512 is broken.

Although only two fuel tanks 500 are shown in FIG. 10, it is clear toone skilled in the art that a third tank, or any number of tanks, may beadded to the fuel tank system without changing the nature of theinvention. This third tank may be connected to either one of the tanks500 shown in FIG. 10 by connecting the third tank to one of the tanks500 by a second connecting line. Similarly, a tee connection may beadded to the connecting line 510, and the second connecting line may beconnected to the connecting line 510 through the tee connection.

It is to be understood that even though numerous characteristics andadvantages of various embodiments of the present invention have been setforth in the foregoing description, together with details of thestructure and function of various embodiments of the invention, thisdetailed description is illustrative only, and changes may be made indetail, especially in matters of structure and arrangements of partswithin the principles of the present invention to the full extentindicated by the broad general meaning of the terms in which theappended claims are expressed.

TABLE 1 DIAMETER OF EACH ORIFICE (cm) Number of Orifices Spring Constant(N/m) in Each Piston 0.5 1.0 2.0 2 A B C 3 D E F 4 G H I

TABLE 2 SPRING CONSTANT [N/m] CRITICAL FLOW RATE ORIFICE SIZE (SQ. CM.)[CUBIC METERS/HR] 0.2 0.4 0.5 5 A B C 6 D E F 7 G H I

1. A system for preventing a fuel spill from a connecting line extendingbetween a first and second reducer fitting on a first and second fueltank, respectively, wherein the first fuel tank is in pressurecommunication with the second fuel tank such that fuel flows from one ofthe first and second fuel tanks to the other when there is a pressuredifference between the pressure acting on fuel in the first fuel tankand in the second fuel tank, the system comprising: (a) a first safetyvalve immersed in the fuel in the first fuel tank, wherein the firstsafety valve has an outlet coupler connected to the first reducerfitting, and wherein the first safety valve has an inlet coupler throughwhich fuel enters the first safety valve; (b) a second safety valveimmersed in fuel in the second fuel tank, wherein the second safetyvalve has an outlet coupler connected to the second reducer fitting, andwherein the second safety valve has an inlet coupler through which fuelenters the second safety valve; and (c) wherein each of the first andsecond safety valves comprises: (c1) a cylindrical housing through whichthe fuel flows, the housing having a diameter; (c2) a piston assemblycomprising: (c2A) a first disc-shaped piston having a diameter slightlysmaller than the housing diameter such that the first piston freelyslides within the housing, wherein the first piston has at least oneorifice defined therein, and wherein the first piston has an upstreamface and a downstream face; (c2B) a second disc-shaped piston positioneddownstream from the first piston, the second piston having a diametersubstantially equal to the first piston diameter, wherein the secondpiston has at least one orifice defined therein, wherein the secondpiston has an upstream face and a downstream face, and wherein fluidentering the safety valve housing exerts a flow force on the firstpiston and the second piston in the direction of fuel flow; (c2C) ashaft connecting the first piston to the second piston; (c2D) a valvestem extending from the downstream face of the second piston, whereinthe second piston is attached to a first end of the valve stem; and(c2E) a stop attached to a second end of the valve stem; (c3) a valveseat with an opening substantially shaped and sized to matingly receivethe stop; and (c4) a spring positioned in the housing against thedownstream face of the second piston assembly such that the springexerts a spring force on the second piston in a direction opposite thegeneral direction of flow, wherein when the flow forces acting on thepiston assembly sufficiently exceed the spring force acting on thedownstream face of the second piston, the piston assembly moves in thedirection of flow until the stop engages the valve seat andsubstantially shuts off the fuel flow to the connecting line.
 2. Thesystem of claim 1 further comprising an alert system to alert a driverof the truck when the connecting line has been severed or detached fromone of the first and second reducer fittings.
 3. The system of claim 2wherein the alert system comprises: a trip wire attached to theconnecting line and extending the length of the connecting line; and anindicator.
 4. The system of claim 3 wherein the alert system furthercomprises electrical wiring to connect the alert system to a battery ofthe truck.
 5. The system of claim 1 wherein the connecting line is aflexible hose.
 6. The system of claim 1 wherein the connecting line is arigid conduit.
 7. A truck fuel tank system, comprising: (a) a first fueltank to contain fuel; (b) a first reducer fitting attached to the firstfuel tank; (c) a second fuel tank to contain fuel; (d) a second reducerfitting attached to the second fuel tank; (e) a connecting lineextending between the first reducer fitting and the second reducerfitting to provide pressure communication between the first fuel tankand the second fuel tank such that fuel flows through the connectingline when one of the first fuel tank and the second fuel tank has morefuel than the other one of the first fuel tank and the second fuel tank;(f) means for preventing a fuel spill when the line is severed ordetached from one of the first reducer fitting and the second reducerfitting: (g) an alert system to alert a driver of the truck when theconnecting line has been severed or detached from one of the first andsecond reducer fittings, wherein the alert system comprises: a trip wireattached to the connecting line and extending the length of theconnecting line; and an indicator.
 8. The truck fuel tank system ofclaim 7 wherein the alert system further comprises electrical wiring toconnect the alert system to a battery of the truck.
 9. The truck fueltank system of claim 7 wherein the connecting line is a flexible hose.10. The truck fuel tank system of claim 7 wherein the connecting line isa rigid conduit.
 11. A containment system for a liquid, comprising: (a)a first tank for containing the liquid; (b) a second tank for containingthe liquid; (c) a connecting line extending between the first tank andthe second tank to provide pressure communication between the first tankand the second tank, wherein liquid flows between the first tank and thesecond tank when one of the first and second tanks has a pressuregreater than the other one of the first and second tanks; and (d) aspill prevention system for shutting off the flow through the connectingline when the flow rate through the connecting line exceeds a specifiedflow rate, wherein the spill prevention system comprises: (i) a firstsafety valve immersed in the fuel in the first fuel tank, wherein thefirst safety valve has an outlet coupler connected to a first reducerfitting, and wherein the first safety valve has an inlet coupler throughwhich fuel enters the first safety valve; (ii) a second safety valveimmersed in fuel in the second fuel tank, wherein the second safetyvalve has an outlet coupler connected to a second reducer fitting, andwherein the second safety valve has an inlet coupler through which fuelenters the second safety valve; and (iii) wherein each of the first andsecond safety valves comprises: (iii1) a cylindrical housing throughwhich the fuel flows, the housing having a diameter; (iii2) a pistonassembly comprising: (iii2A) a first disc-shaped piston having adiameter slightly smaller than the housing diameter such that the firstpiston freely slides within the housing, wherein the first piston has atleast one orifice defined therein, and wherein the first piston has anupstream face and a downstream face; (iii2B) a second disc-shaped pistonpositioned downstream from the first piston, the second piston having adiameter substantially equal to the first piston diameter, wherein thesecond piston has at least one orifice defined therein, wherein thesecond piston has an upstream face and a downstream face, and whereinfluid entering the safety valve housing exerts a flow force on the firstpiston and the second piston in the direction of fuel flow; (iii2C) ashaft connecting the first piston to the second piston; (iii2D) a valvestem extending from the downstream face of the second piston, whereinthe second piston is attached to a first end of the valve stem; and(iii2E) a stop attached to a second end of the valve stem; (iii3) avalve seat with an opening. substantially shaped and sized to matinglyreceive the stop; and (iii4) a spring positioned in the housing againstthe downstream face of the second piston assembly such that the springexerts a spring force on the second piston in a direction opposite thegeneral direction of flow, wherein when the flow forces acting on thepiston assembly sufficiently exceed the spring force acting on thedownstream face of the second piston, the piston assembly moves in thedirection of flow until the stop engages the valve seat andsubstantially shuts off the fuel flow to the connecting line.
 12. Thecontainment system of claim 11 further comprising an alert system toalert a person when the connecting line has been severed or detachedfrom one of the first and second reducer fittings.
 13. The containmentsystem of claim 12 wherein the alert system comprises: a trip wireattached to the connecting line and extending the length of theconnecting line; and an indicator.
 14. The containment system of claim13 wherein the alert system further comprises electrical wiring toconnect the alert system to a battery.
 15. The containment system ofclaim 11 wherein the connecting line is a rigid conduit.
 16. Thecontainment system of claim 11 wherein the connecting line is a flexiblehose.
 17. The containment system of claim 11 wherein the liquidcontained in the tanks is fuel.